Theory of Cowling Channel formation by reflection of shear Alfven wave from auroral ionosphere
Theory of Cowling Channel formation by reflection of shear Alfven wave from auroral ionosphere
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极光电离层反射剪切阿尔文波形成罩盖通道的理论
DOI：
10.1002/jgra.50514
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
A. Nakamizo and R. Fujii
中科院分区：
文献类型：
--
作者：
Yoshikawa A.;O. Amm;H. Vanhamäki;A. Nakamizo and R. Fujii
我们提出了电离层水平电流（包括霍尔电流）和场向电流（FAC）之间通过剪切阿尔芬波耦合的第一个完整公式，它可以描述Cowling通道的形成，而无需对次级（霍尔极化）电场强度进行任何先验参数化。我们的理论重组考林通道的“主要”和“次要”领域。到目前为止，还没有理论框架，可以从观察到的或给定的总电导，电场和FAC分布单独推导出这些分离的组件。而当入射波为阿尔芬波时，反射波可以分解为一次波和二次波。我们表明，反射波可以，根据实际情况，确实进行FAC连接到不同的霍尔电流。通过这种新方法，我们可以确定二次电场变得多大，发散的霍尔电流在电离层内闭合的效率如何，以及有多少霍尔电流作为FAC继续进入磁层。在典型的电离层情况下，只有一小部分FAC以电导梯度连接到霍尔电流，即，次级磁场相对较强。但是，当电导相对较低的阿尔芬电导和/或水平尺度小于10公里，霍尔FAC可能会变得显着。
We present the first complete formulation of the coupling between the ionospheric horizontal currents (including Hall currents) and the field‐aligned currents (FAC) via shear Alfven waves, which can describe the formation of a Cowling channel without any a priori parameterization of the secondary (Hall polarization) electric field strength. Our theory reorganizes the Cowling channel by “primary” and “secondary” fields. Until now there are no theoretical frameworks, which can derive these separated components from observed or given total conductance, electric field, and FAC distributions alone. But when a given incident where Alfven wave is considered as the driver, the reflected wave can be uniquely decomposed into the primary and secondary components. We show that the reflected wave can, depending on actual conditions, indeed carry FAC that connect to divergent Hall currents. With this new method, we can identify how large the secondary electric field becomes, how efficiently the divergent Hall current is closed within the ionosphere, and how much of the Hall current continues out to the magnetosphere as FAC. In typical ionospheric situations, only a small fraction of FAC is connected to Hall currents at conductance gradients, i.e., the secondary field is relatively strong. But when conductances are relatively low compared with Alfven conductance and/or horizontal scales smaller than ~10 km, the Hall FAC may become significant.